A digital raster log image is an image of a paper well logs record in which, along with meta-information about the origin and location of the measurements, multiple curves are displayed on multiple horizontal scales, the vertical scale typically measuring depth which is a measure of distance along a well bore.
There are a large number of potentially valuable historical well log measurements that are recorded on paper or, having originally been recorded on paper, have been scanned to create digital raster images of multiple well logs in a single image. Many of these digital raster images have suffered damage either prior to or during the scanning process and the resulting images exhibit geometric skew (from paper stretching or incorrect scanning), dirt, ink blotches and other image noise that degrades or obscures the desired well log curves. It is desirable to remove or otherwise overcome much of this geometric skew and image noise prior to and as part of the vectorization process.
Well log curve vectorization is most commonly performed by means of a human being expert simply moving a computer mouse sequentially to increasing measured depths to select an ordered sequence of points along a visually evident curve. Because these curves are frequently quite detailed with significant variation from sample to sample, a large number of points along each curve must be manually selected and digitized in order to adequately represent the curve. It is desirable to be able to substantially reduce the number of manually selected points along each curve.
A commercial software product, Neuralog (http://www.neuralog.com/pages/NeuraLog.html), attempts to address the above problem. The product does so by attempting to automatically extend a selected curve to increasing measured depths by image-guided extrapolation. The user selects a point along a curve and the system extrapolates the curve to the end of the image. When the user recognizes that the extracted curve substantially deviates from the visually recognized curve, the user inserts another point and the process is repeated.
In addition, a method for extracting ‘edges’ in 2-D images using a shortest path algorithm exists that was described in an article by E. N. Mortensen and W. A. Barrett, “Interactive segmentation with intelligent scissors” in Graphical Models and Image Processing, 60(5):349-384 (1998). This method, variously known as “Intelligent Scissors” or “Livewire”, has proven useful for image segmentation in the commercial product Photoshop. The method has not, however, been previously employed for extraction and vectorization of well log curves from digital raster log images.